As energy source prices are increasing due to depletion of fossil fuels and interest in environmental pollution is escalating, demand for environmentally-friendly alternative energy sources is bound to play an increasing role in future life. Thus, research into various power generation techniques such as nuclear energy, solar energy, wind energy, tidal power, and the like, continues to be underway, and power storage devices for more efficient use of the generated energy are also drawing much attention.
Specifically, demand for lithium secondary batteries as energy sources is rapidly increasing as mobile device technology continues to develop and demand therefor continues to increase. Recently, use of lithium secondary batteries as a power source of electric vehicles (EVs) and hybrid electric vehicles (HEVs) has been realized and the market for lithium secondary batteries continues to expand to applications such as auxiliary power suppliers through smart-grid technology.
A lithium secondary battery has a structure in which an electrode assembly, which includes: a cathode prepared by coating a cathode active material on a cathode current collector; an anode prepared by coating an anode active material on an anode current collector; and a porous separator disposed between the cathode and the anode, is impregnated with a lithium salt-containing non-aqueous electrolyte.
These lithium secondary batteries are generally manufactured by disposing a polyolefin-based porous separator between a cathode including a cathode active material, e.g., metal oxides such as lithium-cobalt based oxides, lithium-manganese based oxides, lithium-nickel based oxides, or the like, an anode including an anode active material, e.g., carbonaceous materials, and impregnating the resultant structure with a non-aqueous electrolyte containing a lithium salt such as LiPF6 or the like.
When the lithium secondary battery is charged, lithium ions of the cathode active material are deintercalated and then are intercalated into a carbon layer of the anode. When the lithium secondary battery is discharged, the lithium ions of the carbon layer are deintercalated and then are intercalated into the cathode active material. In this regard, the non-aqueous electrolyte acts as a medium through which lithium ions migrate between the anode and the cathode.
Recently, instead of using conventional materials as electrode active materials, research into use of spinel-structure lithium nickel-based metal oxides as cathode active materials or use of lithium titanium oxides and the like as anode active materials has been conducted.
Reaction at an interface between the electrode and the electrolyte varies according to kinds of electrode materials and electrolyte used in the lithium secondary battery. Therefore, there is a need to develop electrolyte techniques that can be suitably adapted to changes in electrode composition.